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Re: Wing calculations 11 Dec 2013 01:48 #659
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Phil, AFAIK, I used the station (STA) of each rib and adjusted the calculations accordingly (calculations are relative to each of the ribs), so I think they are correct, but I'll give another look. Once you get to the fuselage attach, the moment starts to drop i.e. max moment at /sta 8.5 inches, not STA 0
The load that comes from the flaps has to go through the ribs all the way to the spar -- I'll start to look at that next. Cheers, Kenny --- On Tue, 10/4/11, Philip Lardner <This email address is being protected from spambots. You need JavaScript enabled to view it.> wrote: > From: Philip Lardner <This email address is being protected from spambots. You need JavaScript enabled to view it.> > Subject: RE: [Carbondragonbuildersandpilots] Re: Wing calculations, > To: "'Kenny Andersen'" <This email address is being protected from spambots. You need JavaScript enabled to view it.> > Date: Tuesday, October 4, 2011, 9:51 AM Thanks for that Kenny - > > Just going over your numbers, trying to figure out why your rib chords > were so different to mine and I think I've discovered the problem. If > 'Wing STA' > is the distance from the centreline of the glider to each rib, and > each rib is 21.375" apart then the root rib is at 8.5" from the > centreline... the next at 29.875 (not 21.375), the next at 51.25 (not > 42.75, > etc...) Basically > you need to add 8.5" to each rib station to get the correct distance > from the glider's centreline. That done, your spreadsheet (rib chords, > centroids and moments) then agrees with mine... > > ...until I get to the the Cap Loads. For some reason (in my > spreadsheet) I > was dividing the height of the spar by two instead of using the > average distance between the caps. Dumb! > > The next error in my own spreadsheet was in calculating the individual > element loads along the wing. By some aberation I used the Payload > weight (the all-up weight less the wings) instead of the correct > element load I had already calculated. Stupidity. > > Correcting my spreadsheet brings our figures back in line again > (taking into account our slightly different choice of wing loadings.) > > So, two heads really are better than one - thanks for making me > re-check everything and *think*! > > Although I made a couple of fundamental errors in my original > spreadsheet, I'm glad to see that they were on the conservative > side... > waay on the > conservative side! I'm still amazed that even at +10.5g the wing only > needs > 4 rods at the root! > > As you can see, I have calculated the separate rod requirements for > the upper and lower caps. Is there any good reason not do this (i.e. > to keep the number of rods equal for both top and bottom caps)? This > shouldn't be a problem if (as I had planned) you lay the carbon rods > with their widest face > (0.220") flat against the shear web - then your P_cap=M/h is > unaffected by the changing number of rods along the wing. BTW - I'm > using a cap depth (top to bottom) of .220" + (2 x .011") = 0.242" as > the carbon rod caps will be fully enclosed/wrapped in a single layer > of 248 twill cloth, which is 0.011" > per laminate. > > Moving on to the second page of my spreadsheet - the Rib Stress > Analysis - I have run the numbers using the chord of the wing LESS the > chord of the flaperon. I don't know if this is the correct thing to do > or not. I realise that the load generated by the flaperon surface is > transmitted to the main wing through the hinge points but I don't know > how to model that. I would also like to calculate the loads and > stresses along the flaperon surface so I can get an idea of what > materials to use in building them. > > All the best, > > Phil. > > Original Message > From: Kenny Andersen [This email address is being protected from spambots. You need JavaScript enabled to view it.] > > Sent: 03 October 2011 16:06 > To: Philip Lardner > Subject: RE: [Carbondragonbuildersandpilots] Re: Wing calculations > > rect is rectangle, tri is triangle. What I do is calculate the area > of the rectangle between any two of the ribs and then the area of the > (2) triangles (treating is as a single triangle), then I calculate the > centroid individually, and the the centroid of them combined. > The shear is then the > total area times the wing loading and the moment is the total shear > times the distance to the combined centroid from where the section cut > is made. > Once you have the moment, you just divide by the spar cap height > (center of cap to center of cap dist) to get the cap load. Of course, > once you get that you divide by the load/rod to get the number of > rods. Marske did his at 8 Gs, but I think I've seen some 6g gust > loads and since people in sailplanes are actually looking for strong > thermals, and the rods don't add that much mass, then I don't see any > reason to not go the 6g/9g route. > > Again, if you make the spar symmetric, just size the flange with the > compression allowable for the ultimate load, and use that for the > lower (tension dominate) spar so they are both the same. > Kenny > > > --- On Mon, 10/3/11, Philip Lardner <This email address is being protected from spambots. You need JavaScript enabled to view it.> > wrote: > > From: Philip Lardner <This email address is being protected from spambots. You need JavaScript enabled to view it.> > Subject: RE: [Carbondragonbuildersandpilots] Re: Wing calculations > To: "'Kenny Andersen'" <This email address is being protected from spambots. You need JavaScript enabled to view it.> > Date: Monday, October 3, 2011, 8:53 AM > > > > > > > I presume Marske's rod numbers are at 8g, but - wow! > > I'm still working my way through your spreadsheet (thanks for that by > the > way) and comparing it to my numbers (and trying to figure out your > column > headings!) but at +8g I was getting 5 rods on the top cap and 3 rods > on the lower cap at -4g, totalling 104.25ft of rod for both wings (see > attached.) I'll get a bit more time to work on it tonight. > The different > numbers we're getting for our cap loads (you: 9826lbs - > me:19226) is > significant! > > Phil. > > > > From: Kenny Andersen > [This email address is being protected from spambots. You need JavaScript enabled to view it.] > > Sent: 03 October 2011 > 14:16 > To: Philip Lardner > Subject: RE: > [Carbondragonbuildersandpilots] Re: Wing calculations > > > > > > > > Just ran across this > statement about the Monarch, Marske's sail plane with almost > the same span I was looking at the > the number of rods tracks pretty close to the solution I got > 9see below). > The next step is looking at and sizing the spar webs. I was > looking for a hand method to do the webs, but it doesn't look so > good > (easy). However, I do have tools at work that I can use (FEM > stuff). > Maybe Timeshanko has something, but they are always really > complex > (IMO). > > The new Monarch G, a 42.6 ft span sailplane, uses > only four rods (.092 x .220) in each spar cap. Enough rod for > one wing > > panel (upper and lower caps) requires > 112 ft. That amounts to 1.44 lbs > of > rod per wing spar. The total weight of the completed wing spar > is 7 lbs > which includes blocking for root and strut fittings. > > --- On Sun, 10/2/11, Philip Lardner > <This email address is being protected from spambots. You need JavaScript enabled to view it.> > wrote: > > > From: > Philip Lardner <This email address is being protected from spambots. You need JavaScript enabled to view it.> > Subject: RE: > [Carbondragonbuildersandpilots] > Re: Wing calculations > To: > This email address is being protected from spambots. You need JavaScript enabled to view it. > Date: Sunday, October 2, 2011, 5:59 > PM > > > > Hi Kenny, > > I'm sending you the attached > pages > of Marske's manual (off-list, > as it is copyright material) so you > can > see how I am arriving at the > figures in my spreadsheet and other > pages > of notes. > > I'll leave off asking any > questions > until I've had a chance to see your spreadsheet and the > numbers you're > using... but I've already got a few! > > Glad you're on the > mend! > > > Phil. > > > > From: > This email address is being protected from spambots. You need JavaScript enabled to view it. > > [This email address is being protected from spambots. You need JavaScript enabled to view it.] > On Behalf Of > Kenny > Sent: 02 October 2011 13:14 > To: > This email address is being protected from spambots. You need JavaScript enabled to view it. > Subject: > [Carbondragonbuildersandpilots] > Re: Wing > calculations > > > > > > > OK, I FINALLY got a chance to > go over the calculations (the > bronchitis is down to a dull > roar) . I don't have Marske's book, so it > was hurting my brain trying to figure out how he did > everything, so then > I thought, I'd just do it the > 'real' way (LOL). so I just made my > own > spreadsheet and ran the numbers for the wing I was thinking of > it. > Calculate the area, the wing > loading and then the moments and cap > (flange) loads. Our solution > tracked OK until you go to calculate > the > load in the flange. The load in the flange is just the moment > divided by > the height. > > At the root for 8gs you got a moment of 112,951 in-Lb > (I got 109,000). The height of the outer contour is 11.75 at > the root, > but I used 11.5 to account for any offset > > The cap load is then: > 113000/11.5 = 9826 Lb > you got 19226 Lb > > One thing I did to > make sure I didn't get confused is I kept all the units in > inches. I > > upload my spreadsheet once I > get my wing straightened out. I put the > > standard wing on page 1 and > I'll put my wing on page 2. I'm > using: > > pilot weight 220 > parachute 25 > air frame weight > 155 > wing weight -75 > > I'm using 6g limit, 9 g ultimate (that's > the same as an F-16! -- I think it will be enough!) > > A word about > sizing the wing. There is a > couple of things that we can do to > simplify > the analysis and that is a > decision to keep the upper and lower wing > > spar sizing symmetric. It won't cost much weight due to using > the carbon > spar caps. We do that and the > centroid is in the middle and we can > use > P_cap = M/h to calculate the > load in the cap (easy-peeze). > > So you > size just one spar for ultimate load, and that's good enough. > because > carbon fails catastrophically, there is no need to be > concerned about > limit load. Limit load is only used to check for yield. For > virtually > all aerospace-grade aluminum > (other than 6061) , and graphite limit > checks are not necessary. > > Also, I'm going to be a bit more > sporting than my buddy and use 150,000 psi for compression in > the carbon > rod [rather than 100,000] and > just make damn sure I pack everything > right into the corner. Between using the lower allowable and > making the > wing cap sizing symmetric, it > should be plenty conservative. Check > your > spreadsheet for that cap load. > Kenny > > --- In This email address is being protected from spambots. You need JavaScript enabled to view it., > > "Philip Lardner" > <philiplardner@...> wrote: > > > > Ok, > I've updated the Excel > spreadsheet in my files directory with a > new > > sheet detailing the Rib Stress Analysis for each of > the ribs > in the main > > wing. > > > > Phil. > > > > _____ > > > > > From: This email address is being protected from spambots. You need JavaScript enabled to view it. > > > [This email address is being protected from spambots. You need JavaScript enabled to view it.] > > On Behalf Of Philip > > Lardner > > Sent: 28 September 2011 > 16:25 > > To: This email address is being protected from spambots. You need JavaScript enabled to view it. > > > Subject: RE: > [Carbondragonbuildersandpilots] Re: Wing > calculations > > > > > > > > > > > > Hi > Folks, > > > > I've uploaded another few pages of calculations > (Page-20 to Page-23 in the > > 'Phil Lardner' files directory) > covering the rib layout and > stress analysis. > > I've used the root > rib as a worked example and > will upload the numbers for > > the > other ribs when I get them > finished. > > > > I discovered a > few more numerical typos in Jim Marske's text - confirmed by > > > him. The text could also be a > little clearer when describing how the > > rib > > panel centroids are arrived at. I mistakenly used the > > formula on pg D-1 of > > Marske's manual to calculate both centroids > and got answers different to > the > > examples in the text. It took > me a while to discover my error > - the > > centroids are being > measured left and right from > the spar location and not > > just from > the left as on pg. D-1 - hence my drawing on Page-21 showing > the > > > graphical method of finding the centroids! > > > > Comments > welcome... > > > > Phil. > > > > > __._,_.___ > > Reply > to sender | Reply > to group | Reply via web > post | Start a New Topic > Messages in this topic (27) > Recent Activity: > > New Members 1 > New Files 5 > Visit Your Group > > MARKETPLACE > > > Stay on top of your group > activity without > leaving the page you're on - > Get the Yahoo! 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